To an increasing extent, touch-sensitive panels are being used for providing input data to computers, electronic measurement and test equipment, gaming devices, etc. The panel may be provided with a graphical user interface (GUI) for a user to interact with using e.g. a pointer, stylus or one or more fingers. The GUI may be fixed or dynamic. A fixed GUI may e.g. be in the form of printed matter placed over, under or inside the panel. A dynamic GUI can be provided by a display screen integrated with, or placed underneath, the panel or by an image being projected onto the panel by a projector.
There are numerous known techniques for providing touch sensitivity to the panel, e.g. by using cameras to capture light scattered off the point(s) of touch on the panel, or by incorporating resistive wire grids, capacitive sensors, strain gauges, etc into the panel.
US2004/0252091 discloses an alternative technique which is based on Frustrated Total Internal Reflection (FTIR). Light is generated by discrete light sources at fixed locations on the panel. The emitted light is coupled into the panel so as to propagate inside the panel by total internal reflection while expanding in the plane of the panel. Arrays of light sensors are located around the perimeter of the panel to detect the light. When an object comes into contact with a surface of the panel, the light will be locally attenuated at the point of touch. The location of the object is determined by triangulation based on the detected light.
WO2010/006886 discloses an alternative FTIR system, which comprises an illumination arrangement configured to generate and sweep a number of beams of light along an incoupling site on the panel, such that the beams are caused to propagate by TIR in the panel while being swept or scanned across a sensing area on the panel. In the particular FTIR system disclosed in WO2010/006886, one or more light sensors are optically coupled to an elongate outcoupling site on the panel downstream of the sensing area, such that the light sensors are arranged to measure the received energy of the respective beam within the outcoupling site during the sweep. The location of a touching object in the sensing area is determined based on received energy of the respective beam within the outcoupling site as a function of the sweep.
Similar, alternative or supplementary FTIR systems are disclosed in WO2010/006882, WO2010/006884 and WO2010/006885.